The present invention relates to chemical analysis and, more particularly, to devices for injecting samples into analytical equipment. A major objective of the present invention is to provide for improved manual injection of a sample into a gas chromatography (GC) system.
The contributions of the medical, environmental and life sciences to humanity have been facilitated by advances in chemical analysis. Many analytical techniques provide for the division of a complex sample into its components. Gas chromatography is one such analytical technique that separates volatized chemical components according to their relative partitioning between a gaseous mobile phase and a stationary (typically solid) phase. The solid phase is bound within a chromatography column, through which the mobile phase flows. In general, greater separation can be achieved using narrower-bore columns, with capillary separation columns being state of the art.
Especially with capillary columns, the volume and rate of sample introduced are critical. These parameters are best addressed in the context of automated systems. These can inject a sample soon after a needle penetrates an injection septum, and they can inject with high velocities in a repeatable manner. However, an autoinjector may be unavailable for reasons of cost, portability, downtime, and unsuitability for a given task. In these circumstances, manual injection is an attractive and sometimes necessary alternative. However, human physical control tends to be rather gross and slow relative to the demands of capillary GC sample injection. U.S. Pat. No. 6,257,076 to Snyder et al., incorporated by reference in its entirety herein, discloses a manual sample injector that addresses the challenges of precise control over the volume and velocity of injected sample.
There remains a problem, however, regarding the precision with which a sample can be extracted, e.g., from a sample vial into a syringe. For example, if the sample is shallow within a vial, the tip of a syringe needle must be positioned precisely near the base of the vial. In another case, there might be precipitate at the base of the vial that is to be excluded from the sample to be injected into the chromatograph. For another example, it might be desired to extract sample from above or below an interface between two immiscible liquids and avoid the interface itself. Accordingly, what is needed is a manual sample injector that allows precise selection of the location within a vial from which sample is extracted. Furthermore, it is desirable to have this additional control while maintaining the ease of operation associated with the sample injector disclosed in above-referenced U.S. Patent.
The present invention provides a sample injector with an interface-control lever with xe2x80x9cinjectionxe2x80x9d, xe2x80x9cextractionxe2x80x9d and, preferably, xe2x80x9csafetyxe2x80x9d orientations. The interface-control lever orientation determines the limits of relative motion between a syringe holder (and thus a syringe needle) and an interface (and thus a sample vial or an injection port). When the interface-control lever is in the injection orientation, the syringe holder can move to a relative position in which the needle is maximally extended through the interface for injecting a sample into an injection port. When the interface-control lever is its extraction orientation, the syringe holder can move to an extraction position in which the needle extends an intermediate amount from the interface; this intermediate amount is suited for extracting sample from a sample vial and is preferably adjustable. When the interface-control lever is in its safety orientation, the syringe needle is prevented from extending out of the interface, reducing the likelihood of injury to a careless user.
The sample injector includes a plunger driver that grips a syringe plunger, which is used to control sample flow into and out of the syringe. Springs can be used to set default conditions for the interface-control lever, the sample holder, and the plunger driver. An interface-control-lever spring urges the interface-control lever toward its safety orientation. An interface spring urges the syringe holder away from the interface so that the syringe needle is retracted by default. A plunger-driver spring urges the plunger driver toward the sample holder so as to urge the syringe plunger toward its fully inserted position. This spring provides the actual force for sample injection, ensuring a precisely repeatable injection velocity.
The sample injector includes a release lever or other mechanism having cocked and release conditions. When the release is in its release condition, the plunger-driver spring forces the plunger driver to fully insert the plunger. When the release is in its cocked condition, the plunger driver is stopped at a position at which the amount of sample in the syringe is optimized for injection. When from this cocked condition, the release is moved to its release condition, the predetermined amount of sample in the syringe can be injected into an injection port at a predetermined rate by the action of the plunger-driver spring.
Movement of the release from its cocked position to its released position is forced by actuator attached to the interface. As the actuator is moved toward the release, the plunger-driver spring is loaded (deformed so that it applies an increased counterforce). Once the release has been moved past its released position by the actuator, the plunger driver motion is no longer limited by the release. The spring then urges the syringe holder toward the plunger driver. This forces the plunger fully into the syringe so that sample is injected.
The interface assembly ensures alignment of the syringe needle with sample vials (for extraction) and injection septa (for injection). During extraction and injection, the interface assembly typically has a fixed position relative to the injection port or vial. The interface-control lever is configured relative to the interface so that mounting the interface onto a sample vial causes the sample vial to contact the interface-control lever and move it to its extraction orientation. Likewise, the interface-control lever is configured so that mounting the interface onto an injection port (e.g., the septum nut), the injection port contacts the interface-control lever so as to move it to its injection orientation. Thus, the interface-control lever assumes an appropriate orientation automatically.
The sample injector also includes a catch that engages and holds a stop arm of the interface-control lever when the sample injector reaches its extraction condition (with the interface-control lever in its extraction orientation). When the stop arm is so caught, the interface spring cannot force the interface and the sample holder apart so that the needle is fixed in an extended position. This position determines the level of the needle tip within the vial, and thus the vial location from which sample is to be extracted. The catch can be attached to the sample holder and is preferably adjustable so that the extraction position, and thus the vial location from which sample is extracted, can be selected.